Genetic diversity of 96 resynthesized (RS) Brassica napus lines and 25 common (CM) lines were evaluated in present study based on eight main agronomic traits and 315 polymorphic SSR markers. The RS lines were developed through interspecific hybridizations between a vegetable cabbage (B. oleracea L. ssp. alboglabra Bailey) and a number of landraces in B. rapa L. ssp. chinensis and campestris from Southwestern regions of China. The CM lines include 10 elite lines bred in our own Sichuan Agricultural University, 9 elite lines from domestic research institutes in China and 6 exotic spring rapeseed lines from Germany and Canada. The investigated main agronomic traits include plant height, first branch height, main inflorescence length, number of primary branches, siliqua length, seeds per siliqua, siliqua density on the main inflorescence and 1000-seed weight. The observed agronomic traits exhibited a remarkable difference between the RS lines and the CM lines. Large variations were observed in main agronomic traits in the RS and CM lines. A number of salient RS lines were identified, showing variable unique agronomic traits, such as extremely long siliqua length, large 1000-seed weight, high number of seeds per siliqua and high siliqua density, etc. Clustering analyses were made based on both agronomic traits and SSR markers. The UPGMA dendrogram based on the main agronomic traits revealed a major differentiation between the RS lines and the CM lines. The UPGMA dendrogram based on SSR markers clearly distinguished the two main groups of RS lines and CM lines. Large variations and diversities were observed among the RS lines and the CM lines. Big variations were also observed within most of the RS and CM subgroups. We conclude that the RS lines are markedly different from the common (CM) B. napus lines in the study. Large diversity exists among the RS lines and the CM lines. These RS lines could be a valuable source of new germplasm for rapeseed breeding and genetic studies. It is also suggested that the resynthesis of novel B. napus types through interspecific hybridizations with the diverse indigenous B. oleracea and B. rapa sources could be an efficient way to broaden the genetic basis of B. napus L.